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Germanium-assisted growth of titanium dioxide nanowires for enhanced photocatalytic and electron emission performance
(2020-11-15)
Chen, Chih-Yen
;
Lin, Tzu-Chien
;
Chuang, Wen-Shuo
;
Chang, Jeng-Kuei
;
Lee, Sheng-Wei
In this study, free-standing and well-aligned titanium dioxide (TiO2) nanowires were grown on a Ti foil by precisely controlling the growth temperature and the thickness of the Ge catalyst layer. The catalyst layer played an important role in activating the surface of the Ti foil, facilitating the growth of TiO2 nanowires on it in a chemical vapor deposition furnace system. The structure of the TiO2 nanowires was investigated using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The photocatalytic experiment results showed that the optimum Ge catalyst layer thickness significantly improved the rhodamine B (RhB) degradation efficiency of the nanowires. The TiO2 nanowires grown using a 40-nm-thick Ge layer could degrade 74% of RhB after 5 h of ultraviolet irradiation. In addition, the TiO2 nanowires exhibited excellent electron field emission performance as compared to the TiO2 nanocrystals grown without the Ge catalyst layer. The results suggested that TiO2 nanowires grown using a Ge catalyst layer are promising materials for next-generation electronic emitters and photocatalytic systems.
Improved lithium storage capacity and high rate capability of nitrogen-doped graphite-like electrode materials prepared from thermal pyrolysis of graphene quantum dots
(2020-09-10)
Gu, Siyong
;
Christensen, Tommiejean
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Hsieh, Chien-Te
;
Mallick, Bikash Chandra
;
Gandomi, Yasser Ashraf
Adopting a solid-phase microwave-assisted technique followed by thermal pyrolysis of N-functionalized graphene quantum dots, novel nitrogen-doped graphite-like (NGL) electrode materials were synthesized and served as the anode for Li-ion batteries. The NGL anode demonstrated reversible capacity of 530 mAh g(-1) at 0.1C, superior rate capability at high C rate operation (420 mAh g(-1) at 5C), remarkable initial coulombic efficiency (>95.7%), and excellent cyclic stability along with high efficiency (>99.1%) during entire cycling. The NGL anode nanostructure enables improved lithium ion mobility and reversible Li+ storage during cycling. The analysis of the Ragone plots revealed that the specific energy of NGL anode reaches to ca. 840 Wh kg(-1) at the power density of 4200 W kg(-1). The diffusion coefficient of Li ions was measured as 1.69 x 10(-9) cm(2) s(-1) for the NGL anode material, substantially improving over commonly used graphite electrodes (15-26 times higher Li+ diffusivity). The high-rate cyclability as well as the cyclic stability of the NGL anodes were also confirmed via long-term cycling of full pouch cells assembled with ternary cathode and NGL anode. The robust design of the NGL anode materials introduced in this work, paves the way for designing next-generation lithium-ion batteries operating at ultrahigh C rates. (C) 2020 Elsevier Ltd. All rights reserved.
High Power Na3V2(PO4)(3)@C/AC Bi-material Cathodes for Hybrid Battery-Capacitor Energy Storage Devices
(2020-01-08)
Akhtar, Mainul
;
Chang, Jeng-Kuei
;
Majumder, S. B.
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have reported the synthesis and electrochemical characteristics of carbon-coated sodium vanadium phosphate/activated carbon (NVP@C/AC) bi-material electrodes. We have reported that bi-material type NVP@C/AC cathodes offer superior rate performance as compared to either NVP@C or AC electrodes. Through a detailed impedance spectroscopy analyses, we demonstrated that the synergic effect observed in the bi-material electrodes correlates well with the lowering of their charge transfer resistances (R-CT) and the increase of Li(+)diffusion coefficient (DLi+) with the increase of activated carbon content from 0 to 0.60 weight fraction. Through a detailed cyclic voltammogram analyses we have delineated the faradaic and capacitive contribution towards the overall capacities of the bi-material electrodes at various rate conditions. For both these bi-materials, irrespective of the AC content and rate, capacitive contribution dominates the overall capacity. NVP@C/AC40 yields discharge capacities of 67 and 40 mAh g(-1)with capacity retention of more than 93% and 67% after 500 cycles measured at 50 and 1000 mA g(-1), respectively. These bi-materials are demonstrated to be excellent material candidates for high power density lithium titanium oxide (LTO)//NVP@C/AC hybrid battery-capacitor (bat-cap) energy storage devices.
Manipulation of Nitrogen-Heteroatom Configuration for Enhanced Charge-Storage Performance and Reliability of Nanoporous Carbon Electrodes
(2020-07-22)
Sutarsis
;
Patra, Jagabandhu
;
Su, Ching-Yuan
;
Li, Ju
;
Bresser, Dominic
In this study, various nitrogen-containing functional groups, namely, pyridine (N-6), pyrrole (N-5), oxidized N (N-O), and quaternary N (N-Q), are created on activated carbon (AC) surface via melamine, ammonia, and nitric oxide doping methods. N-5 and N-6 groups markedly alter the specific surface area and pore size of AC. N-O is found to affect electrolyte wettability, and the N-Q content is closely associated with AC electronic conductivity. The nitrogen-containing groups do not contribute to pseudocapacitance in propylene carbonate and acetonitrile electrolytes. However, the nitric-oxide-treated carbon (AC-NO) exhibits the best highrate charge-discharge performance among the investigated materials. The N-Q-enriched and N-5/N-6-depleted AC-NO most effectively suppresses the leakage current and gas evolution of supercapacitors. Online gas chromatography is used to analyze the gaseous species produced from AC electrodes. With an appropriate surface functionality on carbon, the cell voltage can be increased to similar to 3 V, increasing the energy and power densities. The aging behavior of the carbon electrodes with and without nitrogen modification after being floated at 2.5 V and 70 degrees C for 3 days is investigated. An effective strategy for enhancing supercapacitor performance and reliability is proposed.
Ga-doped lithium lanthanum zirconium oxide electrolyte for solid-state Li batteries
(2020-09-01)
Mishra, Mrinalini
;
Hsu, Che-Wei
;
Rath, Purna Chandra
;
Patra, Jagabandhu
;
Lai, Hong-Zheng
Cubic-phase Li7La3Zr2O12 (LLZO) garnet is a promising solid electrolyte candidate for next-generation Li batteries. As a viable approach, the desired cubic-phase formation of LLZO relies on elemental doping. In this regard, various dopants such as Al and Ga are doped into the LLZO samples, which are synthesized using a solid-state reaction method. The Al-and Ga-doped LLZO can transform to a cubic-phase garnet at 900 degrees C. After 1200 degrees C sintering, a Li2ZrO3 impurity phase is found for the Al-doped LLZO pellet, which still shows many voids and inhomogeneous particles on the surface. The Ga doping seems to be attractive since it can effectively stabilize the cubic phase and desired microstructure within 900-1200 degrees C. Based on the optimized Ga-doped LLZO (LGLZO), various electrolyte architecture designs are developed that include LGLZO pellet electrolytes with and without poly(ethylene oxide) (PEO)-lithium bis(tri-fluoromethylsulfonyl)imide (LiTFSI)-LGLZO coating, and hybrid electrolyte layers of PEO-LiTFSI, PEO-LGLZO, and PEO-LiTFSI-LGLZO composites. Li//LiFePO4 (LFP) cells with various types of electrolytes are assembled, and their charge-discharge properties are investigated. The all-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell exhibits satisfactory charge storage performance, which has revealed potential for practical applications. (c) 2020 Elsevier Ltd. All rights reserved.
Physicochemical and electrochemical properties of the (fluorosulfonyl) (trifluoromethylsulfonyl)amide ionic liquid for Na secondary batteries
(2020-09-15)
Yang, Huan
;
Luo, Xu-Feng
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Matsumoto, Kazuhiko
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Chang, Jeng-Kuei
;
Hagiwara, Rika
In this study, thermal, physical, and electrochemical properties of the ionic liquid electrolyte system, Na[FTA]-[C(3)C(1)pyrr][FTA], (FTA(-) = (fluorosulfonyl) (trifluoromethylsulfonyl)amide and C(3)C(1)pyrr(+) = N-methyl-N-pro-pylpyrrolidinium) have been investigated for Na secondary batteries. The asymmetric FTA. structure provides a wide liquid-phase temperature range, especially at low x(Na[FTA]) (x(Na[FTA]) = molar fraction of Na[FTA]) and low temperature range. Glass transition at 170-209 K is the only observed thermal behavior in the x(Na [FTA]) of 0.0-0.4. Temperature dependence of viscosity and ionic conductivity obeys the Vogel-Tammann-Fulcher equation, and the correlation between molar conductivity and viscosity follows the fractional Walden rule. The anodic potential limits are above 5 V vs. Na+/Na at 298 and 363 K. The noticeable effects of x(Na [FTA]) are observed in the electrochemical performance of Na metal and hard carbon electrodes. In both cases, a moderate concentration, x(Na[FTA]) of 0.2-0.3, enables favorable charge-discharge behavior. At 363 K, the discharge capacities of the hard carbon electrode at x(Na[FTA]) of 0.3 are 260 and 236 mAh g(-1) at the current densities of 20 and 200 mA g(-1), respectively. The optimum cycling performance occurs at x(Na[FTA]) = 0.3, providing satisfactory capacity retention and high average Coulombic efficiency.
A Holey Graphene Additive for Boosting Performance of Electric Double-Layer Supercapacitors
(2020-04-01)
Huang, Jun-Bin
;
Patra, Jagabandhu
;
Lin, Ming-Hsien
;
Ger, Ming-Der
;
Liu, Yih-Ming
We demonstrate a facile and effective method, which is low-cost and easy to scale up, to fabricate holey graphene nanosheets (HGNSs) via ultrafast heating during synthesis. Various heating temperatures are used to modify the material properties of HGNSs. First, we use HGNSs as the electrode active materials for electric double-layer capacitors (EDLCs). A synthesis temperature of 900 degrees C seems to be optimal, i.e., the conductivity and adhesion of HGNSs reach a compromise. The gravimetric capacitance of this HGNS sample (namely HGNS-900) is 56 Fg(-1). However, the volumetric capacitance is low, which hinders its practical application. Secondly, we incorporate activated carbon (AC) into HGNS-900 to make a composite EDLC material. The effect of the AC:HGNS-900 ratio on the capacitance, high-rate performance, and cycling stability are systematically investigated. With a proper amount of HGNS-900, both the electrode gravimetric and volumetric capacitances at high rate charging/discharging are clearly higher than those of plain AC electrodes. The AC/HGNS-900 composite is a promising electrode material for nonaqueous EDLC applications.
A Lithium-Ion Rechargeable Full Cell Using the Flower-like Na3V2(PO4)(3)@C Cathode and Li4Ti5O12 Anode
(2020-05-18)
Akhtar, Mainul
;
Pradhan, Sunil Kumar
;
Chang, Jeng-Kuei
;
Majumder, Subhasish Basu
;
材料科學與工程學系
In the present work, we have demonstrated that nanopetal-assembled hierarchical carbon-coated Na3V2(PO4)(3) (nNVP@C) microflowers, synthesized via a microwave-assisted hydrothermal route, play an important role for yielding superior electrochemical characteristics of a Li4Ti5O12 (LTO)//nNVP@C full cell. Thus, the full cell yields superior power density with decent discharge capacity after extended cycling and good rate performance. The nanosize petals help Li+ to diffuse faster in NVP particles, and the inner mesoporous morphology of microflowers allows the electrolyte to easily penetrate into the embedded NVP@C nanocrystals. Furthermore, the homogeneous carbon coating provides an elastic buffer to mitigate the strain developed during Na+ extraction and subsequent Li+ insertion and extraction. The LTO//nNVP@C full cell is claimed to be suitable for power applications, where relatively thinner electrodes would be flooded with a sufficient amount of the lithium salt-containing organic electrolyte. To improve the cycleability characteristics, one requires to match carefully the Li+ activity in the organic electrolyte with electrode capacity. This would ensure stoichiometric lithium-ion insertion in the LTO electrode together with predominant lithium-ion insertion in the nNVP@C cathode.
Facile synthesis of core-shell structured Si@graphene balls as a high-performance anode for lithium-ion batteries
(2020-05-07)
Jamaluddin, Anif
;
Umesh, Bharath
;
Chen, Fuming
;
Chang, Jeng-Kuei
;
Su, Ching-Yuan
Encapsulating silicon (Si) nanoparticles with graphene nanosheets in a microspherical structure is proposed to increase electrical conductivity and solve stability issues when using Si as an anode material in lithium-ion batteries (LIBs). Currently the main strategies to produce high-quality Si-graphene (Si@Gra) electrodes are (1) chemical vapor deposition (CVD) of graphene grown in situ on Si by hydrocarbon precursors and (2) encapsulating Si with a graphene oxide followed by postannealing. However, both methods require a high-temperature and are costly and time-consuming procedures, which hinders their mass scalability and practical utilization. Herein, we report a Si@Gra composite with a ball-like structure that is assembled by a facile spray drying process without a postannealing treatment. The graphene sheets are synthesized by an electrochemical exfoliation method from natural graphite. The resulting Si@Gra composite exhibits a unique core-shell structure, from which the ball-like morphology and the number of graphene layers in the Si@Gra composites are found to affect both the electric conductivity and ionic conductivity. The Si@Gra composites are found to increase the capacity of the anode and provide excellent cycling stability, which is attributed to the high electrical conductivity and mechanical flexibility of the layered graphene; additionally, a void space in the core-shelled ball structure inside the Si@Gra compensates for the Si volume expansion. As a result, the Si@few-layer graphene ball anode exhibits a high initial discharge capacity of 2882.3 mA h g(-1) and a high initial coulombic efficiency of 86.9% at 0.2 A g(-1). The combination of few-layer graphene sheets and the spray drying process can effectively be applied for large-scale production of core-shell structured Si@Gra composites as promising anode materials for use in high-performance LIBs.
Hydrous ruthenium oxide-tantalum pentoxide thin film electrodes prepared by thermal decomposition for electrochemical capacitors
(2020-07-01)
Xie, Jian-De
;
Hsu, Kai-Hsiang
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Patra, Jagabandhu
;
Su, Ching-Yuan
;
Lee, Sheng-Wei
In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2-Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 degrees C preserves a large fraction of hydrous RuO2 center dot xH(2)O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2-Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg(-1) at a power density of 8720 W kg(-1) (or 8.3 Wh L-1 at 15,000 W L-1). In addition, an excellent durability of 97.6% capacitance retention after 3000 charge-discharge cycles is found for this electrode. The proposed RuO2-Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.

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